1. Field of the Invention
The present invention relates generally to an index scan system in a video tape recorder (referred to as VTR hereinafter), and more particularly, to an index scan system in a VTR comprising an index scan function of searching at high speed the starting portion of each program recorded on a magnetic tape in response to an index signal indicating the starting position of the program and a picture-in-picture function (referred to as PIP function hereinafter) of forming a video signal for picture-in-picture display to output the same.
2. Description of the Prior Art
The conventional VTR of a VHS (Video Home System) type includes a VTR comprising a so-called index scan function of performing pulse-width modulation of a control signal in response to an index signal indicating the starting position of each program recorded on a magnetic tape and recording the same, to search the recorded program utilizing such an index signal. As such an index scan function, a VISS (Video Index Search System) utilizing only an index signal or a VASS (Video Address Search System) utilizing an address signal indicating an absolute address of a tape in addition to the above described index signal is generally employed. The VTR with such an index scan function is described in, for example, Japanese Patent Laying-Open Gazette No. 201249/1984 and "Electronics Life", Journal issued by NHK, Mar. 1987, pp. 123-126.
More specifically, in the VTR with the above described index scan function, a control track having a control signal recorded thereon is formed on a magnetic tape to control traveling of the tape. The duty ratio of the control signal (pulse) is changed depending on, for example, the data contents of an index signal so that the starting position of each recorded program is indicated. More specifically, in such a VTR even in a fast forward mode (FF mode) or a rewind mode (REW mode) in which a tape is travelled at high speed by half-loading control, the tape is travelled with a control head for recording and reproducing of a control track being contact with a control track of the tape. In particular, when an index scan mode is set, the change of the duty ratio of the control signal, i.e., the index signal is detected by the control head during high-speed traveling of the tape, so that the tape is controlled to be travelled in a normal reproducing mode only in a short time period (for example, for five seconds) by reversing the tape by a constant amount or without reversing the tape every time the index signal is detected, to reproduce the starting positions of the recorded programs in order.
On the other hand, the conventional VTR includes a VTR comprising a PIP function of performing time-base compression of either one of a video signal reproduced from a magnetic tape and a video signal received by a TV tuner contained in the VTR or a video signal externally inputted and combining the same with the other video signal, to form a video signal for picture-in-picture display in which a subscreen is inserted into a part of a main screen and output the same. The VTR with such a PIP function is described in, for example "Sanyo Technical Review" issued February 1987, Vol. 19, No. 1, pp. 76-84.
The conventional VTR with the above described index scan function is adapted such that the output of the received video signal is interrupted to output the reproduced video signal every time the index signal is detected during the index scan mode. More specifically, monitoring of the screen caused by the received video signal or the externally inputted video signal is interrupted every time the recorded program is reproduced, which is very inconvenient for practical usage.
Additionally, a VTR has been put into practice in which reproduced pictures are sequentially reduced and displayed every time the index signal is detected, to form a plurality of subscreens without forming the above described main screen in the VTR with the above described index scan function. Such a VTR is disclosed in, for example, Japanese Patent Laying-Open Gazette No. 141873/1987. However, in such a VTR, the screen caused by the received video signal from the contained TV tuner or the externally inputted video signal.